1. Field of the Invention
The present invention relates to an additive which can increase the fluidity of an aqueous polyurethane dispersion and is useful for preparation of aqueous polyurethane dispersion with high solid content.
2. Description of the Related Art
A polymer of polyurethane (PU) is polymerized by a bi- or multi-functional isocyanate and a polyol. The characters of PU can be changed by varying the chemical structure or ratio of isocyanate and polyol. The structure thereof includes soft segments with low glass transition temperature and hard segments with high polarity, wherein the soft segments are made from polyol with high molecular weight and has the characters of flexibility, rubber-like and non-crystal as well as high extensibility under low stress. Also, the hard segments are crystal, polar and short segments mainly constructed by amino acid ester groups made from the interaction between isocyanate and polyol with low molecular weight and has the characters of non-deformation under extension. The different properties between soft and hard segments result in the microphase separation structure of PU. Moreover, the ratio of isocyanate and polyol can be changed to obtain various properties, such as products with various degree of hardness including elastic body with extreme softness or extreme hardness. Therefore, said PU can be applied to mobile industry, engineering, furniture, wearing, fitness equipment, adhesive agent and etc. Recently, said PU is also used for development and application of biomedical materials and intelligent materials (shape memory polymers).
According to the internal emulsifier used, aqueous polyurethane can be distinguished into non-ionic or ionic type. Ionic aqueous polyurethane can be further distinguished into anionic or cationic type. Common internal emulsifier includes non-ionic coupling agent such as 1,4-butanediol (1,4-BD), cationic internal emulsifier such as methyldiethanolamine (MDEA) and anionic internal emulsifier such as dimethylol propionic acid (DMPA) and 2,2-bis(hydroxymethyl)butyric acid (DMBA).
According to the dispersion character resulted from different solvents used in an polyurethane, polyurethane can be distinguished into aqueous or organic solvent type. Since the aqueous polyurethane has the advantage of good environmental concern and low-cost resulting from reducing the use of organic solvent, it becomes the most of current applications. Common preparation of aqueous polyurethane includes acetone process, prepolymer mixing process, melting dispersion process and etc. The aqueous polyurethane prepared is in the form of emulsion, and the solid content thereof can be adjusted according to its application. Unfortunately, increasing solid content could result in decreasing in fluidity of an aqueous polyurethane dispersion. Therefore, it is an important task for the art to increase the solid content of an aqueous polyurethane dispersion without decreasing the fluidity thereof.